The following abbreviations are utilized herein:
3G third generation of GSM-based mobile networks
ASIC application specific integrated circuit
AWGN additive white Gaussian noise
BC broadcast
BER bit error rate
BPSK binary phase-shift keying
BS base station
CDMA code division multiple access
CF compress-and-forward
CSI channel-state information
DF decode-and-forward
DSP digital signal processor
Eb/N0 energy per bit per noise power spectral density
EF estimate-and-forward
E-UTRAN evolved universal terrestrial radio access network
FDMA frequency division multiple access
FPGA field programmable gate array
IEEE institute of electrical and electronics engineers
LDPC low-density parity-check
LLR log-likelihood ratio
MA multiple access
Node B base station
OFDMA orthogonal frequency division multiple access
p.d.f. probability density function
QAM quadrature amplitude modulation
QPSK quadrature phase-shift keying
SFN single frequency network
SNR signal to noise ratio
SQ scalar quantization
TDMA time division multiple access
UE user equipment, such as a mobile station or mobile terminal
VQ vector quantization
WAN wide area network
WCDMA wideband code division multiple access
WiMAX worldwide interoperability for microwave access (IEEE 802.16 standard)
WLAN wireless local area network
In communication systems, relay nodes or devices, also referred to as repeaters, may be used in a variety of ways. Generally, a relay device is configured to receive and transmit, or re-transmit, a signal. Three types of relay devices are briefly considered here. A first type of relay receives a signal, amplifies the signal and re-transmits the amplified signal. The first type of relay is relatively transparent and primarily repeats the input signal. A second type of relay receives the signal, decodes the input signal, possibly performs some processing on the decoded data, re-encodes the data and transmits the re-encoded data. The second type of relay acts in a manner similar to a BS. Note that the second type is generally more complex than the first type as it processes the input signal in some fashion. A third type of relay is one that falls between the first and second types. For example, a third type relay may receive an input signal and regularly re-transmit only a portion of the input signal. As another example, a third type relay may receive an input signal, process the input signal to obtain information about the received signal and transmit the obtained information. As an example, the information may be a reduced or simplified version of the input signal (e.g., a digitized or quantized version of the input signal).
One example of a third type relay utilizes a CF (i.e., EF) relay protocol, where the relay quantizes its received signal and forwards the quantized output to the destination.
In a wireless communication system having an intermediate relay node, if the relay node is unable to decode a received signal reliably, it may form an estimate and forward the estimate to the destination. Generally, this estimate may be obtained by quantization or compression. Conventional quantization techniques include distortion-minimizing quantization and non-optimized uniform quantization (e.g., analog-to-digital converters).